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P Collins, 1996, "SPS 2000 and its Internationalisation", Engineering Construction and Operations in Space 5, ASCE, Vol 1, pp 269-279.
Also downloadable from http://www.spacefuture.com/archive/sps 2000 and its internationalisation.shtml

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SPS 2000 and its Internationalisation
Abstract

The paper describes the "SPS 2000" system currently being designed to operate as a pilot plant delivering 10 MW of microwave power from low Earth orbit to receiving antennas at the Earth‘s surface. Research under way on different aspects of the satellite and the ground segment, and field research under way in a number of equatorial countries is described. A number of issues other than the technical design of the system which are also of importance both in planning the system and in assessing its potential value, are also discussed.

Introduction

Research on delivering energy from space to the Earth started at the Institute for Space and Astronautical Science (ISAS) in 1981, and there has been an annual Space Energy Symposium at ISAS since then. In 1987 the SPS Working Group was started as a working group under the Space Engineering Committee at ISAS, which is a loose association of researchers in universities, companies and research centers who are interested in studying various aspects of the SPS concept.

As part of the work of this group, four research projects were conceptualized - the ”Energy Mission• for the SFU reusable satellite; the ISY/METS microwave energy transmission experiment which was performed using a sounding rocket in 1993; the "Microwave Garden• environmental impact research project currently under way; and an SPS "Strawman• project. The "SPS 2000• project initially grew out of the last of these; it was felt that, by studying a real case, researchers would obtain information about practical problem areas of SPS development.

The basic motivation behind the SPS 2000 project was to find an answer to the question "What is a Solar Power Satellite?• Many people in the space industry are of course familiar with the concept of SPS. However, when this question was asked by engineers in the electricity supply industry, the only answer available was the SPS "Reference System• designed as part of the US Department of Energy‘s work in the 1970s. Although that study advanced research on many aspects of SPS, it created a very specific picture of an extremely large-scale system which might be feasible only about 50 years in the future. Clearly this does not provide a practical target for electricity companies to aim at in the near future: just as if the Wright brothers had started by proposing a 500-passenger long range aircraft. Consequently the primary objective of the SPS 2000 study has been to create a realistic and practical concept of an SPS that could be built in the near future.

In order to achieve this, a firm guideline was prepared for researchers. This was necessary because the electric power industry is very different from space engineering, and space system designers have no experience of terrestrial power system design. The guideline comprised the following six requirements, which are described in more detail in (1).

SPS 2000 Requirements

  1. The first phase of construction should Start in the year 2000. This gives the study a realistic background, and leads to the requirement that it should deliver no more than 10 MW. This is large by comparison with existing satellites, but if it were much smaller it would not be of interest to electricity companies.

  2. Commercial technologies are to be used. This means that effort must be made to use existing products where possible; to avoid new technology development as far as possible; and technologies used must be cheaply mass-producible.

  3. The electricity generated should be competitive with existing small scale electricity generation. If SPS-generated electricity is not cost-competitive with other electricity sources it will not be developed. This is a very difficult target for the space industry which has a tradition of very high costs, but real progress must be made in this direction. So the cost target set for the SPS 2000 satellite is to be able to sell microwave energy to rectenna operators at 10 Yen/kWh. NB the launch cost is treated separately.

  4. The SPS 2000 satellite will be placed in a low equatorial orbit by commercial launch systems. Launch provision and electricity supply are quite separate businesses, and companies building SPS satellites in future will buy launch services from commercial launch companies. Following the same pattern, the SPS 2000 satellite is being designed to be launched by existing vehicles. For the time being, the Ariane 5 and Proton launch vehicles are used as candidates for sizing the satellite modules.

  5. Customers for the power generated by SPS 2000 will be people living close to the equator. Only equatorial orbits enable the satellite to deliver power several times per day to the same receiver. Coincidentally, the equatorial regions of many countries are poor, and lack electricity supplies. Thus, although the SPS 2000 project will supply only approximately 100 kW as a continuous supply, this could be enough to supply several hundred households.

  6. The initial 10 MW system will he designed to allow system growth in the future. SPS 2000 is not considered to be an optimum design for SPS in future. Consequenfly the design of the SPS 2000 system must take into account the possibility of including new technology in future, as well as expansion to larger units, higher orbits, and other possibilities.
Current system design

Following these guidelines, the project progressed, and won a prize in 1991 for being the best proposal to be made at the " SPS 91• international conference in Paris (2). The newsletter "SPS 2000 News" was started in 1992. The 1st phase of the conceptual design of the overall system was completed in 1993, and a report was published and submitted to the SPS Working Group (3). Functional working models of the SPS 2000 system were built and exhibited in 1994 and 1995, and a Home Page on Internet was opened in 1995 (4).

Design

The current design comprises a satellite in the form of an equilateral triangular prism some 303 m in length, and with sides of 336 m. The structure is a light-weight aluminium framework to be assembled in orbit by autonomous assembly robots. The frame carries some 9 hectares of solar panels on two sides (see Figure 1). On the horizontal base it carries a phased-array microwave antenna 132 m square, comprising some 17,000 1-meter-square panels (see Figure 2).

Figure 1. SPS 2000 satellite structure
Figure 2: Microwave beam transmission
Figure 3: SPS 2000 System
Ground stations

Microwave power receiving antennas, "rectennas", are also needed at a number of sites around the equator. These comprise a microwave receiving surface; an electric power collection system; a pilot beam system to provide a signal for phase-control of the microwave power beam; and an electric power processing system and delivery network (see Figure 3). In addition, because the satellite will deliver power for some 200 seconds as it passes overhead once during each orbit of approximately 100 minutes, it will be necessary to store the energy received by the rectenna, and deliver it continuously as a supply of perhaps 100 kW (5).

The size of the rectennas will vary from one site to another, but may be of the order of 1 km in diameter (6). At date of writing, preliminary field research visits have been made to 3 countries, Tanzania, Papua New Guinea and Brazil (7). It is hoped eventually to make such agreements with perhaps 8 different countries. The use of the power produced will vary from site to site, making each rectenna system a separate design project.

Outstanding work

To date many different aspects of the system design have been studied in detail, and work is continuing on these. In addition, by studying such a near-term SPS design many problem areas have been identified which require further study, as described in (1).

International field research

In 1994 the Japanese Ministry of Education provided a research grant for field research in a number of equatorial countries (8). The objectives of this research are to make contact with appropriate counterparts in a number of equatorial countries; to have initial discussions with government representatives in those countries; to identify some candidate rectenna sites; to develop preliminary ideas about appropriate rectenna designs for each site; and to consider how each rectenna might best he utilised.

For potential users of the power produced by the SPS 2000 system, the most important issues are separate from those of satellite design. In the design of the ground segment the major issues include selecting a rectenna site and deciding the size of the rectenna; selecting the most appropriate designs for the microwave reception sub-system and the rectenna structure; calculating the actual amount of energy that will be received; estimating the most attractive 24-hour pattern of electricity supply for potential users in the neighbouring district; calculating the appropriate size for the electricity storage system and the amount of electric energy that will be available for use; planning the electricity distribution network and its operation; and estimating the overall cost of the ground segment. In the mechanical design of the rectenna, practical engineering issues, such as the problem of birds nesting on the rectenna, or of cattle rubbing against the support structure, are also important.

The first field visits have been to Tanzania, Papua New Guinea and Brazil. In each of these countries, contacts have been made with researchers in universities, government research centers, and with appropriate government staff and business people. In each of these countries also, one or more potentially attractive sites have been identified for rectennas. In all the countries there is enthusiasm to participate in the SPS 2000 project, and collaboration between staff in these countries and in Japan will continue in order to make more concrete designs for the rectenna system. Until it is decided that the SPS 2000 project will go ahead, only limited resources can be used. However, even at the present stage preparatory research is needed to plan rectennas, since in the absence of clear prospects of successfully installing, using and maintaining sufficient rectennas, it will not be possible to be confident of the value of the overall project. In each country visited, as well as visiting relevant government offices and research centers, it is also necessary to visit regions close to the equator, since the satellite can deliver only to sites at less than about 3 degrees latitude.

Tanzania

The first field visit was made to Tanzania in September and October 1994. One of the largest countries in east Africa, Tanzania has an area of almost 1 million square kilometers, and a population of about 25 million people. Visits were made in the capital Dar es Salaam to the Ministry of Water, Energy and Minerals, the Directorate of Meteorology, Tanzania Electricity Supply Company, Tanzania Communications Commission, the Commission for Science & Technology, the University of Dar es Salaam and other organisations. In all cases there was interest in Tanzania participating in the SPS 2000 project.

A visit was then made to a region north of Kilimanjaro and Mount Meru, where a wide plain extends up to the border with Kenya. An attractive site for a rectenna was found between Mount Longido and the small border town of Namanga. The land has thin tree cover, and is used mainly for grazing of nomadic herds of cattle. A design in which the rectenna surface is raised perhaps 2-3

meters above the ground would allow cattle to pass freely underneath (see figure 4). Visits were also made to the Arusha office of the National Land Use Planning Commission, and the nearby National Radiation Commission. In future work, the lead is to be taken by the Faculty of Electrical Engineering of the University of Dar es Salaam (9).

Figure 4: SPS 2000 rectenna on Longido Plain
Papua New Guinea

A country comprising both continent and pacific islands, Papua New Guinea (PNG) has an area of almost 0.5 million square kilometers, and a population of some 4 million people. Independent of Australia for some 20 years, PNG has substantial mineral resources, and fertile land. In February and March 1995 visits were made to a number of government offices in the capital, Port Moresby, including the Department of Village Services and Provincial Affairs, the Prime Minister‘s Office, the Department of Energy Development, and the Spectrum Management Department of the Post and Telecommunication Corporation. A number of issues were discussed and the staff were all interested in PNG participating in the SPS 2000 project.

Visits were then made to potential rectenna Sites in four different northern provinces within a few degrees of the equator - New Zealand, Manus, East Sepik and Sandaun. The conditions of a rectenna sited in PNG would be interestingly different from Longido Plain, since the climate would be maritime, and the rectenna might be sited over trees or short crops. In addition there is periodic torrential rain which may affect the microwave power transmission. Finally a visit was made to the University of Technology (Unitech) in the city of Lae, where the Department of Electrical and Communications Engineering agreed to lead further study of a PNG rectenna (10).

Brazil

The largest country in South America, Brazil has an area of 8.5 million square kilometers and a population of some 150 million people. The northern part of the country stretches for more than two thousand kilometers along the equator. Being a much larger country than Tanzania and Papua New Guinea, with a longer history of economic development, Brazil has a long-established space research center (INPE), a civilian space agency (AEB), and an equatorial launch site (CLA) for which it is developing a satellite launch vehicle, due to fly for the first time in 1996.

Visits were made in September and October 1995 to several INPE sites, to the headquarters of the Brazilian space agency, AEB, and to the launch center at Alcantara near Sao Luis. In all of these there was considerable interest in the SPS 2000 project. The Director-General of AEB offered to coordinate Brazilian participation in SPS 2000, and to collaborate with the Ministry of Energy and other appropriate organisations to study the possibilities. Thus, although details remain to be decided, there is a possibility that Brazil may participate in the SPS 2000 project by hosting a rectenna; by doing research on the ionospheric impact of the SPS 2000 microwave power beam; and also by utilising the launch center at Alcantara (11).

Issues arising

A number of issues that require further study were identified during the field visits to date, and others are expected to arise in future. First, although the frequency range between 2.4 and 2.5 GHz is defined by the International Telecommunications Union (ITU) as the Industrial Scientific & Medical (ISM) band, it is also used for telecommunications in some countries, including Tanzania and Papua New Guinea. Thus there is a need to solve any interference problems that SPS 2000 might cause for these Systems in equatorial countries.

Secondly, in districts where there is currently no electric power, the first priority is often for electric lighting in the evenings. Consequently the SPS 2000 rectenna output may be used primarily in the evenings. In this case the energy storage system would need to be several times larger than for supplying power evenly through the day.

Third, since the rectennas will be like a wire mesh, and will permit sunlight to pass through and reach the ground, the approximately 1 sq km of land needed for a rectenna could also be used for agriculture. It will therefore be desirable to plan the use of the land beneath the rectenna in combination with planning the rectenna itself.

Fourth, as more detailed plans for each site are developed, there will be increasing collaboration between researchers in Japan and in the equatorial countries, and also between the equatorial countries, which have common interests and can learn from each other. This is encouraged through the Newsletter "Equatorial Times•. As the number of participating countries grows and their contribution to the project increases, the influence of the ground segment on the project will grow, and the views of SPS 2000 users, the customers for the power produced, will grow more important.

Fifth, in Brazil there is already considerable expertise in ionospheric research, centered on study of the anomalies in the magnetic equator over Brazil. Using this expertise to study the impact of the SPS 2000 microwave beam on the ionosphere near the equator would be a unique opportunity for advancing SPS research in general.

Economics

The economics of SPS in general are conveniently expressed in the following equation:

C(el) = C(r cap) + C(r op) + P(mw)
C(el) is the cost per kWh of electricity; C(r cap) is the rectenna capital cost per kWh of electricity produced; C(r op) is the rectenna operating cost per kWh produced; and P(mw) is the price paid by a rectenna user to a satellite operator for each kWh of microwave "fuel" delivered to the rectenna. If electricity companies build rectennas and link them to their existing electricity grids, then, since they know the cost of electricity from other generation systems, once they know the cost of a rectenna they can calculate the price that they can afford to pay for microwave power from space.

In this context, by building and operating the SPS 2000 system, a wealth of real information on the cost of rectennas will be accumulated. This will enable operators of SPS 2000 rectennas to offer prices for microwave power from space from other suppliers than the SPS 2000 satellite. Although, as discussed below, the SPS 2000 rectennas will be much more expensive per kWh of output than future commercial SPS rectennas, since they will be constructed as part of a research project, the capital cost will not have to be recovered from electricity sales.

An important point is that this offer would represent a real commercial price. That is, if a space engineering company were to design and build a satellite capable of delivering microwave power to the required specification, each SPS 2000 rectenna user-group could become their customer. Users could even sign firm contracts in advance guaranteeing to purchase microwave power, which could facilitate the satellite companies obtaining investment. By offering a real price in this way, users of SPS 2000 rectennas will create the first commercial demand for microwave energy from space, which will give a clear and concrete target for space engineering companies to aim for.

In view of current commercial plans for constellations of LEO telecommunications satellites (which is itself stimulating the development of low-cost launch vehicles), it is conceivable that such companies might consider building a constellation of LEO satellites to provide more power to the equatorial SPS 2000 rectennas. In view of the further possibility of low-cost reusable launch vehicles being developed in the foreseeable future, it is possible to conceive a development route from SPS 2000 to future, fully commercial, large-scale SPSs.

SPS 2000 Costs

The objective of SPS research is to develop an economical,environmentally benign, large-scale source of electricity supply for the Earth. The cost target for the SPS 2000 satellite, excluding launch costs, is ¥9 billion ($90 million), although the current cost estimate is considerably higher (1). Such a cost would be more or less competitive with terrestrial solar photovoltaic systems today, and is based on a proposed price of ¥10/kWh for the microwave energy delivered from space.

Cost estimates for SPS 2000 rectennas have not yet been made. However, we know that SPS 2000 rectennas would not be economic sources of electricity - even if they received microwaves without charge - for three main reasons.

1st, the utilisation rate of each rectenna will be low, some 3%, since the satellite will be in low Earth orbit, and will not remain stationary.

2nd, the intensity of the microwave beam will be only 10W/sqm in the centre of the beam, which is within international safety standards today. By contrast, it is proposed that future commercial Systems should have intensities as high as several hundred W/sqm.

3rd, in order to produce a continuous power output, electricity storage capacity will be required, which will raise the cost of the rectenna system and introduce losses which would not apply to a future commercial rectenna.

Thus, among other things, it would not be realistic to expect developing countries which have a shortage of electricity to pay for the construction of SPS 2000 rectennas. If the project is realised, the capital cost of the rectennas which are not likely to be a major part of the overall cost will probably be treated as part of the project cost.

For future commercial Systems, the cost per kW of rectenna capacity will be much less than SPS 2000, and we can envisage that any country that wishes to use electricity from space will construct a rectenna and buy microwave power from SPS satellites. Interestingly, many developing countries will have economic advantages in this; their land and labour costs are both low, so constructing rectennas will be considerably cheaper than in more economically developed countries. In addition, the market price of electricity in many developing countries is higher than in richer countries, due to the inadequate supply. Consequently, in a future global market for microwave power from space, developing countries will be able to offer very competitive prices.

Although the primary objective of SPS is engineering research through operating a real pilot plant, it will in fact provide electricity to people living in developing regions, at a cost subsidised by the advanced country that builds the satellite (12). In future, countries that are capable of paying for microwave supplies from space will do so on a commercial basis. The extent to which subsidies may be provided by richer countries to certain rectenna-using countries will be a political decision, depending on a range of factors including the political relations between the countries in question, and the benefits to the richer countries of developing SPS as a major energy source.

Future Developments

One objective of follow-on systems will clearly be to provide more power at lower cost than SPS 2000. However successor projects will also have engineering objectives, like SPS 2000, which will justify some research expenditure beyond the purely commercial value of their output.

Multiple satellites

Probably the easiest way of upgrading the system would be to launch several identical satellites into the same orbit. With no further investment at the rectenna site, the average output would be doubled with two satellites, trebled with three satellites, and so on. In order to utilise the power it would be necessary to increase the capacity of the power supply network, but the rectenna microwave and electrical susbsystems, and the power conditioning and storage systems might not need alteration. The main difference would be that the stored energy would be discharged at higher rates over a wider network than in the initial case. By contrast, increasing the size of a single satellite would require increasing the storage capacity of the rectenna The ultimate development in this direction would be a system of some 30 satellites delivering microwaves almost continuously during the day at each rectenna, using storage only for backup supply.

Higher orbits

Microwave power satellites in higher orbits would have longer delivery periods, shorter night-time periods, and a wider latitude range within which countries could participate in rectenna operation. However, in higher orbits, satellites would orbit within the Earth‘s radiation belts, which will cause faster degradation. However, being able to supply microwave power to a wider range of latitudes is attractive in increasing the number of countries that would gain operating experience of SPS systems.

Larger satellites

Larger satellites would have greater output, but greater storage capacity would be needed at the rectenna. Building larger satellites would be of interest in progressing towards future, large-scale commercial systems, but would not be as economical as several smaller satellites in the same orbit.

More intense microwaves

The intensity at the center of the SPS 2000 microwave beam is only 10 W/sqm, which is the internationally accepted safety level for continuous wave radiation at 2.45 GHz, as used in microwave ovens. However, in order to make better use of the rectennas, some satellite makers may offer to deliver more intense microwave power beams, as is proposed for future, large-scale commercial SPSs. This will require both redesign of the rectennas, and establishment of a number of specifications and standards.

Non-equatorial orbits

In addition, to using satellites in geo-stationary orbit, there is a wide range of possible configurations of future systems for delivering power from space to Earth, including Molniya orbits, systems sited on the Moon, and even at the Sun-Earth Libration Point 1. The choice between such possibilities will ultimately be made according to the cost of the electricity produced (other factors such as environmental impacts being judged acceptable). For interim projects, high inclination orbits such as the Molniya orbits might be interesting in facilitating power delivery to high latitude sites in developed countries.

Electricity industry participation

Depending on the relative success of SPS 2000, the situation would be ripe for electricity supply research funding to be used to advance SPS. Perhaps focussing initially on studies of optimal rectenna designs, electricity company researchers could play a wide range of useful roles, as discussed in (13). In particular, due to their large resources, both technical and financial, electricity companies could be expected to rapidly advance SPS studies which have received minimal funding to date, once the feasibility of the system is demonstrated. Indeed, electricity companies are already contributing to the development of microwave power transmission and reception technology, such as Kansai Electric Power Company‘s collaboration with Kyoto and Kobe universities (14).

Reusable launch vehicles

Official interest in developing fully reusable launch vehicles has increased considerably recently, with the flights of the DC-X experimental vehicle in the USA; NASA‘s $130 million budget for RLV studies; plans for the X-33; and publication of the design of the " Kankoh-maru• passenger-carrying vehicle (14). If reusable launch vehicles are to obtain certification like commercial aircraft, there will be a need for hundreds of test flights, like aircraft. These flights will be available for carrying cargo to LEO at costs well below those of existing expendable launch vehicles. Thus, future progress of such projects may offer the possibility of low-cost launch for modules of SPS 2000 and its successors.

Institutional Impacts

If SPS 2000 is developed it will have a range of important international institutional impacts. In particular, it will create a small but nevertheless real international customer base, a professional rectenna engineering community within the international electricity industry, and a focus for international media attention - none of which exist today. In addition, in order for the system to develop further, technical specifications will be needed for microwave power transmission from space, leading to the development of internationally agreed standards for this new international industry.

International Customer base

Demand for a product or service is the foundation of a business. In the case of SPS, more than 25 years after the initial proposal there is still no demand for microwave power from space. By starting to create real demand on Earth for microwave power from space, SPS 2000 will alter this situation radically for the better. Based on their experience, users of SPS 2000 rectennas will be able to offer firm prices for supplies of microwave power from space. These prices will be higher the more valuable is the supply in terms of intensity, duration, quantity, reliability, and so on. The existence of a real customer base will therefore give the space engineering community clear financial targets for the development of SPS.

Rectenna engineering profession

A growing professional community around the world with expertise in planning, designing, building, operating, maintaining, and evaluating operational SPS rectenna systems will generate great

interest among electricity companies in every country. To date, electricity company researchers have been understandably lukewarm about theoretical proposals for far-future space power systems. The extremely high cost of today‘s space projects does not give them confidence that energy from space could be economic. SPS 2000 will create actual operating rectennas for them to assess. This will provide a simple interface for the space engineering community who will be able to gain credibility by delivering microwave power to the electricity industry‘s specifications.

International media focus

SPS 2000 rectennas will demonstrate repeatedly the reception of several MW of safe, clean, silent electric power from space, and will provide a focus for media attention world-wide. Today the option of SPS as a future large-scale source of electricity is not widely known in the world; for the media it remains simply another "paper idea•. Actually demonstrating a real system will prove that it is a real energy option; will provide the media with interesting real-life material; and will create a clearer image for them of possible future SPS systems. In addition, each rectenna will be a different "story•. In the modern media-dominated age this will lead to a great increase in popular interest in SPS and the many space developments to which it is linked.

Technical specifications for commercial microwave power from space

In order for SPS 2000 to operate, international agreement on the utilisation of the appropriate electromagnetic frequency will be necessary. This will concern primarily the equatorial and near equatorial countries, whether or not they operate a rectenna. Negotiations on this matter will primarily be through the International Telecommunications Union (ITU), possibly through a subcommittee established for the purpose, which is responsible for international management of the utilisation of the electro-magnetic spectrum.

In addition, in order to purchase power from satellites other than SPS 2000 it will be necessary to establish technical specifications for the microwave power that the SPS 2000 rectennas will accept. On the basis of their combined experience, the equatorial community of SPS 2000 rectenna users will in effect decide the specifications for the microwave power that they will be prepared to buy from orbital suppliers. For example, the maximum intensity at the centre of the SPS 2000 microwave beam is within current international safety limits for continuous exposure of the general public. For future systems the intensity at the center of the beam, to which humans will not be exposed, will probably be considerably higher. However, this will require safeguards to ensure that the microwave intensity outside the rectenna does not exceed acceptable limits. These conditions will be described in the specifications for microwave energy supplies that the users of SPS 2000 rectennas will wish to purchase. Such specifications will be an indispensable guide for space engineering companies interested in supplying this market.

International standards for microwave power from space

This work may progress as far as establishing international standards for microwave power from space. This would be a major undertaking, involving international negotiations not only among equatorial countries and the ITU, but also other interested countries, prospective makers, owners and operators of microwave power generating satellites, electricity companies, environmental agencies, airlines, national and international air traffic control authorities, insurance companies and other interested organisations both national and international.

The necessary international standards would cover such aspects as safety, environmental impacts, power distribution within the main beam and sidelobes, reliability, stability, electro-magnetic interference, use of air-space and orbital space, and other matters. Establishing such a standard would represent an achievement of great significance, that could become the basis of a future global space power industry.

Conclusions

The SPS 2000 study is currently at too early a phase for a decision to be made whether it should be realized or not. However, work is currently progressing well, not only in solving the problems arising in designing the satellite, but also in planning the ground segment comprising a family of rectennas sited in countries around the equator.

If the project is realised, it could lead on to a range of further developments, which could become a path leading from SPS 2000 to full-scale, commercial SPSs. It will also have a wide range of international institutional impacts. Consequently, if the SPS 2000 project is realised it will not only play a historic role in being the first SPS, but it may also lead on to the creation of a commercial SPS industry. For those who are optimistic about the prospects for SPS becoming a major new source of energy for the Earth, and therefore a major source of commercial revenues for space engineering companies, this also means that SPS 2000 will play a historic role in humans‘ future expansion into space. For this reason, the further internationalization of the project is highly desirable, in order that as many countries as possible have the satisfaction of playing a part in this development of such long term importance.

References
  1. M Nagatomo et al, 1994, "Conceptual study of a solar power satellite SPS 2000", Proc. 19th ISTS
  2. M Nagatomo and K Itoh, 1991, "An evolutionary satellite power system for international demonstration in developing countries", Proc. SPS 91, pp 356-363
  3. SPS 2000 Task Team, 1993, " SPS 2000 Project Concept", S2-Tl-X, ISAS
  4. http://spss.isas.ac.jp
  5. H Matsuoka et al, 1995, " Aspects of SPS 2000 Rectenna Planning", RCAST, University of Tokyo, Matsuoka Laboratory Working Paper 3
  6. T Shima et al, 1995, " Simulation of the output power of SPS 2000 rectennas", Proceedings of 2nd WPT Conference
  7. H Matsuoka and P Collins, 1995, " Field Research for SPS 2000 rectennas in equatorial countries", Proceedings of 2nd WPT Conference
  8. SPS 2000 Task Team, 1994, " SPS 2000 Project: Research on Power from Space for Equatorial Countries", Ministry of Education, Science and Culture Research Grant No.06041022.
  9. H Matsuoka et al, 1994, " Field Research for Solar Power Satellite Energy Receiving Stations: Tanzania", RCAST, University of Tokyo, Matsuoka Laboratory Working Paper 1
  10. H Matsuoka et al, 1995, " Field Research for Solar Power Satellite Energy Receiving Stations: Papua New Guinea", RCAST, University of Tokyo, Matsuoka Laboratory Working Paper 2
  11. H Matsuoka et al, 1995, " Field Research for Solar Power Satellite Energy Receiving Stations: Brazil", RCAST, University of Tokyo, Matsuoka Laboratory Working Paper 5
  12. M Nagatomo, 1995, "An approach to develop space solar power as a new energy system for developing countries", Journal of Solar Energy, in press
  13. P Collins, 1994, " Towards commercial electricity from Space", 13th ISAS Space Energy Symposium, pp 28-31
  14. J Taki, 1994, " Microwaves seen as key transmitters", Nikkei Weekly, December 5
  15. K Isozaki et al, 1994, " Considerations on vehicle design criteria for space tourism", IAF paper no. 94-V.3.535
P Collins, 1996, "SPS 2000 and its Internationalisation", Engineering Construction and Operations in Space 5, ASCE, Vol 1, pp 269-279.
Also downloadable from http://www.spacefuture.com/archive/sps 2000 and its internationalisation.shtml

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